Genetic and phenotypic studies of hypomorphic lin-12 mutants in Caenorhabditis elegans.

The lin-12 gene of Caenorhabditis elegans is thought to encode a receptor for intercellular signals that specify certain cell fates during development. We describe several alleles of lin-12 that reduce but do not eliminate lin-12 activity (hypomorphic alleles). These alleles cause a novel egg-laying defective (Egl) phenotype in hermaphrodites as well as incompletely penetrant cell fate transformations seen with high penetrance in lin-12 null mutants. Characterization of the Egl phenotype revealed additional roles of lin-12 in the development of the egg-laying system that were not apparent from studying lin-12 null mutants: lin-12 activity is required for proper early vulval morphogenesis as well as for some unknown later aspect of egg-laying system development. Reversion of the Egl phenotype caused by one lin-12 hypomorphic allele was used to identify potential interacting genes as described in the accompanying paper.